A proximity sensor is a sensor that is able to detect the presence of nearby objects without any physical contact. One particular type of proximity sensor emits a beam of electromagnetic radiation in the infrared spectrum, and detects changes in the field or return signal. The object being sensed may be referred to as the proximity sensor's target. To test such a sensor, a target is selected that has sufficient reflection characteristics in the infrared spectrum used by the sensor. The target is then placed at different distances from the sensor, while measuring the output of the sensor. As the target is moved farther away, the output of the sensor drops. Typically, the sensor is tested at several different target distances, and if its output falls outside an expected range for each target distance, then the sensor may be deemed a failing unit.
While the proximity sensor has long had several applications, its relatively recent use in personal mobile communications devices such as cellular phones and smart phones that have a touch sensitive display screen presents a particularly difficult challenge for its high volume manufacture testing. Smart phones such as the iPhone™ device by Apple Inc. use a proximity sensor to detect when the user has moved the device to her ear during a call, and on that basis may decide to disable any input from a touch screen to avoid inadvertent touch commands being entered due to contact with the user's cheek. Quality control may call for each specimen of such a smart phone device to be tested prior to sale. Since a relatively large number of such specimens may need to be released to end users over a short time interval, for example every day, a more efficient test methodology for testing the proximity sensor is needed.